1. Field of the Invention
The present invention relates to an inspection apparatus and, more particularly, to an apparatus and method for inspecting polycrystalline silicon (Poly-Si) using illuminated and reflected light.
2. Discussion of the Background
Generally, a thin film transistor (TFT) comprising Poly-Si has about 10 to 100 times mobility of a TFT comprising amorphous silicon (a-Si). Therefore, the Poly-Si TFT is typically used for a pixel switching device and for a peripheral driving circuit in a liquid crystal display (LCD) and organic EL display devices, allowing development of an integrated TFT-LCD with simultaneously formed pixel and driving circuit TFTs on the same substrate. FIG. 1 shows a TFT that may be used in an integrated LCD or organic EL display device.
FIG. 1 is a cross-sectional view illustrating a typical TFT.
Referring to FIG. 1, a buffer layer 2, made of an insulating material such as silicon oxide (SiO2), is formed on an insulating substrate 1, and a semiconductor layer, made of Poly-Si with a mean grain diameter of 0.24 μm˜0.45 μm, is formed on the buffer layer 2. Implanting impurities in the semiconductor layer forms a channel 3 and drain and source regions 4 and 5.
A gate insulating layer 6 is formed on the entire surface of the semiconductor layer, and an interlayer insulating layer 7 is formed on the gate insulating layer 6. Drain and source electrodes 10 and 9 are connected to the drain and source regions 4 and 5 via contact holes 12 and 11, respectively. A gate electrode 8 is formed on the gate insulating layer 6 over the channel 3.
The Poly-Si forming the semiconductor layer may include various sized grains in a range of several nm to μm by means of an excimer laser annealing (ELA) process. Protrusions (P and P′ in FIG. 2A and FIG. 2B, respectively) may be formed in the Poly-Si grain boundary based on the crystallization method.
FIG. 2A shows the formed protrusions P having a consistent interval therebetween, and FIG. 2B shows the formed protrusions P′ having an inconsistent interval therebetween.
When displaying an image on an organic EL display device or an LCD device fabricated with Poly-Si having inconsistently formed protrusions as shown in FIG. 2B, a plurality of thin stripes may be generated on the screen, thereby deteriorating image quality. On the other hand, fabricating a display device using Poly-Si having consistently formed protrusions, as shown in FIG. 2A, may significantly reduce the stripes.
Therefore, good and bad quality products may be identified by measuring the distance between the Poly-Si protrusions. Therefore, an inspection apparatus that is capable of measuring the distance between the Poly-Si protrusions is desired.